The report of the eight-year-old girl's diagnosis comes after choking smog enveloped the northeastern city of Harbin two weeks ago, bringing flights and ground transport to a standstill and forcing schools to shut for several days.

Visibility in some areas reduced to less than 50 metres.

At the height of the smog, the city's levels of PM2.5 - the smallest, most dangerous type of airborne particle - reached 1,000 micrograms per cubic metre or 40 times the World Health Organisation's recommended standard.

High levels of PM2.5 have been linked to health problems including lung cancer and heart disease.